Conventionally, the technology of using the signal light of wavelength in the 1.31 μm and 1.55 μm band in optical communications is established.
The optical fiber which has been mainly used as an optical transmission line in optical communications is a standard Single Mode Fiber (SMF) having zero dispersion wavelength in the 1.31 μm band. (1.3 μm band corresponds to the wavelength band of 1300-1324 nm, hereinafter).
Moreover, the transmission loss of silica, which is the base material of an optical fiber, is minimum in the 1.55 μm band. Combining with the development of the Erbium Doped Fiber Amplifier (EDFA) to carry out high efficient optical amplification in the 1.55 μm band, the Dispersion Shifted Fiber (DSF) which has zero dispersion wavelength in the 1.55 μm band has been recently commercialized as an optical transmission line for wavelength division multiplexing (WDM) transmission. (1.55 μm band corresponds to the wavelength band of 1530-1570 nm, hereinafter.).
However, when the SMF having zero dispersion wavelength in the 1.31 μm band is used as an optical transmission line, too low dispersion in the 1.31 μm band tends to result in Four Wave Mixing (FWM) in the 1.31 μm band, which is one of the nonlinear phenomena, and on the other hand too large dispersion in the 1.55 μm band makes it difficult for WDM transmission in a wide band.
Meanwhile, when the DSF having zero dispersion wavelength in the 1.55 μm band is used as an optical transmission line, too low dispersion in the 1.55 μm band tends to result in FWM in the 1.55 μm band, which is one of the nonlinear phenomena, and on the other hand too large dispersion in the 1.31 μm band makes it difficult for WDM transmission in a wide band.
The U.S. Pat. No. 5,905,838 discloses the optical fiber, which enables WDM transmission in both the wavelength bands of 1.31 μm and 1.55 μm.
In the optical fiber disclosed by the U.S. Pat. No. 5,905,838, the absolute value of dispersion is made low in both the wavelength bands by shifting the zero dispersion wavelength into the range between 1350 nm and 1450 nm, and reducing the dispersion slope in both the 1.31 μm and 1.55 μm band.
The fiber enables a data-transmission capacity of 100 or more channels with a transmission speed of 2.5 Gbps without employing dispersion compensation in a relatively short distance system, applicable for metropolitan area.